package j04updown;

class Ye{}
class Fa extends Ye{}
class Ch extends Fa{}

class Man<T>{}

public class J1 {
    public static void main(String[] args) {
        Man<Ye> m1 = new Man<>();
        Man<Fa> m2 = new Man<>();
        Man<Ch> m3 = new Man<>();

        //上界
        Man<? extends Fa> m0 = m2;
        m0 = m3;
//        m0 = m1;

        //下届
        Man<? super Fa> mx = m2;
        mx = m1;
        //*
        mx = new Man<Object>();
    }
}
